1. Field of the Invention
This invention relates to methods of producing green ceramic tapes and more particularly, to producing such tapes without the use of organic solvents.
2. Description of the Prior Art
Green ceramic tapes have hitherto been prepared using a binder prepared by dissolving a resinous binder such as a butyral resin or the like in an organic solvent such as methyl ethyl ketone, adding the binder solution to a fine ceramic powder and mixing for an extended period of time to prepare a slip, deaerating the slip, and coating the slip onto a substrate using a doctor knife to prepare a tape, and then drying the tape by application of heat.
However, the use of an organic solvent in the conventional process has certain drawbacks such as toxicity and offensive odor perceptible by people in the vicinity of the factory, as well as the danger of explosion which is present with volatile solvents. Accordingly, a method of preparing green ceramic tapes has recently been proposed which employs an aqueous organic binder such as polyvinyl alcohol or polyvinyl acetate, or the like, instead of the organic solvent-based binder.
Although the use of an aqueous-based binder is desirable from the point of view of eliminating the drawbacks of organic solvent-based binders, some problems are still encountered. Among these problems are coagulation of the fine ceramic powder in the slip, deviation of the viscosity of the slip from Newtonian flow, poor fluidity of the slip and poor dispersibility of the ceramic material, and difficulty in forming green tapes having high density and smooth surfaces.
Hence, a need continues to exist for a method of forming green ceramic tapes of high quality without the use of an organic solvent-based binder.